1. Field of the Invention
The present invention relates to a focus adjusting device for cameras having a varifocal optical system in which the focusing position for a subject at a given distance alters with the movement of a zooming lens group of the system for varying its focal length, and the amount of focusing movement of a focusing lens group of the system varies with the focal length.
2. Description of the Prior Art
As disclosed in U.S. Pat. No. 3,850,507 and U.S. Pat. No. 3,930,720, there have been proposed focus adjusting devices for such varifocal optical systems which are capable of adjusting the position of the focusing lens group with zooming operation to compensate for the variation in the focusing position of the lens group. These focus adjusting devices are provided circumferentially within a lens barrel or provided in a portion of a lens barrel radially projected therefrom. Accordingly the lens barrel has an increased outside diameter, or the barrel is partly bulged to accommodate the device and therefore has a peculiar shape which appears unsightly. The diametrically or locally enlarged lens barrel is difficult to handle and inconvenient to use. Moreover neither of the focus adjusting devices is suited to automatic focusing because it is extremely difficult to couple the device to an automatic focusing means incorporated in a camera body.